This invention relates to an aerial conveyor system and particularly to an aerial conveyor system that is especially useful in conjunction with strip mining operations.
Strip mining is carried out by removing a layer of material, commonly referred to as "overburden", in order to expose an ore-bearing layer. The ore-bearing layer is then removed using one or more of several conventional techniques depending upon the particular mining operation. Following the mining operation, the excavation may either be refilled or allowed to fill with water.
Although generally more economical than subsurface mining operations, the strip mining procedures in use at the present time typically involve a number of highly disadvantageous characteristics. First, it will be appreciated that in those instances in which the ore-bearing layer to be mined extends over a substantial distance, it is at least theoretically possible to utilize overburden removed from a particular area to refill a previously mined area of the excavation. This possibility has heretofore not been fully utilized in view of the fact that the equipment available to carry out the operation has been less than wholly satisfactory.
For example, systems for refilling strip mining excavations have been constructed using conveyors. However, the conveyors presently available for use in these systems comprise apparatus extending first down one side of the excavation, then along the bottom, and then up the other side. Such equipment is unsatisfactory both because it is unduly expensive and because it is unduly cumbersome to reposition as the excavation of the mine continues.
It is also possible to utilize dump trucks or similar vehicles to convey the newly excavated overburden material to the refilling location. However, this too has proved both unduly costly and cumbersome due to traffic problems which are encountered when a large number of dump trucks are employed in a mining location.
An even more important considereation in the refilling of a strip mining excavation is based on ecological factors. Regardless of whether conveyors or dump trucks are utilized to transport the excavated overburden material to the refilling location, it is presently necessary to refill the previously mined portion of the excavation in substantially reverse order from that in which the overburden material is removed. This means that the topsoil layer is deposited on the bottom of the excavation, followed by the next adjacent subsoil layer, etc. In many instances the net result of this procedure is that the material comprising the surface of the refilled area is not of a type which is capable of sustaining trees and grass, crops, or other vegetation. There is thus produced a substantial desert which is of no practical value.
The present invention comprises an aerial conveyor system which is useful in strip mining operations to eliminate the foregoing and other problems long associated with the prior art. In accordance with the broader aspects of the invention, an aerial conveyor is suspended between two vehicles located on the opposite sides of a strip mining excavation. The first vehicle is positioned adjacent the side at which overburden is being removed from the excavation, and includes apparatus for delivering excavated material to the conveyor. The second vehicle is utilized to position the discharge end of the conveyor over a previously mined portion of the excavation.
The use of the invention is advantageous from a number of standpoints. First, by means of the invention there is provided a system for transporting excavated overburden to a refilling location which does not involve the expense and repositioning difficulties of prior conveyor systems and which simultaneously eliminates the expense and traffic problems encountered when dump trucks are utilized to perform this function. Second, by means of the invention the overall costs of a strip mining operation is substantially reduced. Finally, by means of the invention it is possible to refill the excavation in exactly the same order in which the overburden was removed therefrom. That is, the refilled portion of the excavation is characterized by having topsoil at the upper surface thereof, whereby the process of returning the mined area to productive usage is greatly facilitated.
In accordance with the broader structural aspects of the invention, the aerial conveyor system comprises at least one cable suspended between the two vehicles. A substantially rigid conveyor support structure is supported by the cable and extends from a receiving zone adjacent the first vehicle across an open area of the excavation to a discharge zone. A plurality of spaced apart, substantially transversely disposed conveyor support rollers are mounted on the support structure, and an endless conveyor belt is mounted for movement around a course defined by the conveyor support rollers. The conveyor belt functions to transport material received in the receiving zone from the delivery means of the first vehicle across the open area of the excavation and to discharge the material in the discharge zone.
In accordance with more specific aspects of the invention, the conveyor support structure comprises a plurality of conveyor support frames each including a plurality of hook rollers engaging one of the cables and a pair of elongate members supported by the hook rollers and extending substantially parallel to the cables. The conveyor support frames are mounted end to end, and the elongate members of the conveyor support frames are interconnected to define an array of conveyor support frames which is substantially rigid and which extends from the receiving zone across the open area to the discharge zone. The conveyor support frame at the discharge zone end of the array supports a drive roller and a drive motor which actuates the drive roller to move the conveyor belt around the course. In accordance with one embodiment of the invention, operating power for the drive motor is supplied from the receiving zone end of the array of conveyor support frames through tubular passageways extending through the elongate members thereof.
In accordance with still other aspects of the invention, the conveyor support frame at the discharge end of the array is secured against relative movement with respect to the cable. The receiving zone end of the conveyor system is secured to the first vehicle by means of a bogie comprising levers having upper and lower ends. The levers are pivotally supported on the first vehicle at a point intermediate the upper and lower ends, and the cables and the receiving zone ends of the array of conveyor support frames are secured to the upper and lower ends of the levers, respectively. By this means the bogie functions to vary the tension on the conveyor belt in accordance with the total weight of material being transported by the conveyor system.
In accordance with another embodiment of the invention, the conveyor support structure comprises a conveyor support frame including a pair of elongate members extending substantially parallel to the cables from the receiving zone to the discharge zone. The conveyor belt support rollers are mounted transversely between the elongate members. The cables are adapted with a plurality of spaced pulleys along the length thereof, and the elongate members are adapted with a plurality of pulleys along their length. A support cable is threaded alternately between the cable pulleys and the pulleys of the elongate members such that the elongate members are suspended from the cables. The support cables are adjustable such that the elongate members, and thus the conveyor belt, may be raised and lowered relative to the cables by adjusting the length of the support cables.
In one embodiment of the invention, the elongate members comprise an array of tube members, with the tube members being engaged end to end with structure for permitting axial movement of the receiving zone end of the conveyor belt relative to the discharge zone end to permit tensioning of the belt. In another embodiment of the invention, cables are substituted for the tube members to make up the elongate member of the conveyor support frame. In each of the embodiments, the conveyor system is inwardly collapsible and is maintained in the extended position from the receiving zone end to the discharge zone end by applying an axially outwardly directed force on the ends of the conveyor system.
The present invention is further directed to numerous arrangements for controlling the tension on the conveyor belt in relation to the load being carried on the conveyor belt. These systems are designed to increase the tension on the conveyor belt as the loading on the belt increases and to reduce tension on the belt as the load on the conveyor belt is lightened. In one embodiment of the invention, the power required to drive the conveyor belt is monitored, and the structure for controlling the tension on the belt is adjusted in accordance with the required driving power in order to appropriately tension the belt.